Quantum Computation and Quantum Coherence in Mesoscopic Josephson Junctions

Jian Zou, Bin Shao

D. V. Averin

Amitabh Joshi

Rosanna Migliore, ANTONINO MESSINA, Anna Napoli

D. V. Averin

Recent experimental demonstrations of quantum coherence of the charge and flux states of Josephson junctions show that the quantum Josephson dynamics can be used to develop scalable quantum logic circuits. In this work, I review the basic concepts of Josephson tunneling and Josephson-junction qubits, and discuss two problems of this tunneling motivated by quantum computing applications. One is the theory of photon-assisted resonant flux tunneling in SQUID systems used to demonstrate quantum coherence of flux. Another is the problem of quantum measurement of charge with the SET electrometer. It is shown that the SET electrometer at the Coulomb blockade threshold is the quantum-limited detector with energy sensitivity reaching ħ/√3 in the resonant-tunneling regime.

Kuang Le-Man, Wang Yiwen, Mo‐Lin Ge

In this paper, we study the supercurrent in a mesoscopic Josephson junction (MJJ) and its quantum statistical properties in the presence of nonclassical light fields. We investigate in detail the influence of external nonclassical light fields on current-voltage step structures of the MJJ. We also study in detail quantum statistical properties of the supercurrent when the external quantum electromagnetic fields are even and odd coherent-state light fields. It is shown that the supercurrent in the MJJ exhibits both squeezing effect and quantum coherences. It is demonstrated that the MJJ can feel the difference not only between classical light fields and nonclassical light fields but also between different nonclassical light fields.